Parathyroids and ultimobranchial bodies in monotremes

Abstract

Only scant information is available in the scientific literature on the parathyroids and ultimobranchial bodies in the primitive mammals, the echidna (Tachyglossus aculeatus) and platypus (Ornithorhynchus anatinus). The major aim of this paper is to describe the morphology of the monotreme parathyroid gland and to compare it with parathyroids in mammals and reptiles. The gross anatomy and light microscopic structure of the ultimobranchial body, thymus, and thyroid are also given. Animals were dissected and routine light and electron microscopic techniques used to examine the microscopic morphology. The locations of parathyroid hormone, calcitonin and calcitonin gene-related peptide in tissue sections were identified by immunostaining. Monotremes have one pair of parathyroid glands located in the thorax and they are often associated with thymic tissue but never with the thyroid which is also present in the mediastinum. Ultimobranchial bodies are ventrolateral to the commencement of the trachea. Thymic lobules with Hassall's corpuscles are scattered in the fibrofatty tissue of the mediastinum and the ventral surface of the pericardium. Histologically, principal cells, water-clear cells, and non-secretory cells were identified in the parathyroid glands. Principal cells showed polarity and had microlamellar projections that formed intercellular canaliculi. Non-secretory cells had features similar to those of thymic epithelial reticular cells. Immunostaining of parathyroid hormone showed a diffuse distribution in parathyroid principal cells and none in ultimobranchial bodies. Identification of the ultimobranchial bodies was confirmed by immunostaining. The monotreme parathyroid gland, ultimobranchial bodies and thyroid show reptilian as well as mammalian features.

Arteries define the position of the thyroid gland during its developmental relocalisation

“…In most vertebrates, two thyroid lobes are positioned cranial to the aortic arch, midway along the carotid arteries, as is the case in mice and humans (Pischinger, 1937). Conversely, in some vertebrates such as crocodiles, turtles, and certain mammals as the echidna (Haynes, 1999;Pischinger, 1937), a single-lobed thyroid is positioned further caudally at the aortic arch, at the base of the branching carotid arteries (Fig. 6).…”

Hormonal Control of Ca Homeostasis in Lower Vertebrates: Considering the Evolution

“…We have so far clarified the primary structure of the calcitonin of the stingray, goldfish, sardine and bullfrog by the purification technique of peptides (Takei et al, 1991;Sasayama et al, 1992 andSuzuki et al, 1994;Yoshida et al, 1997). We have also reported the nucleotide sequence of the calcitonin of 4 species of primitive bony fishes, 6 species of amphibians, and 4 species of reptiles by PCR, RT-PCR and RACE-PCR methods 1999;Sakamoto et al, 1999). These studies have demonstrated that calcitonin of primitive bony fish such as lungfish has been conserved from fishes to reptiles and that reptile calcitonin is almost the same as that of chicken.…”

“…Recently, in monotremes: namely the platypus (Orinithorhynchus anatinus) and the echidna (Tachyglossus acleatus), the anatomy and morphology of the ultimobranchial glands, the thyroid gland, and the parathyroid glands were studied (Haynes, 1999). In these animals, one pair of the parathyroid glands did not connect to the thyroid gland but to the thymus, which is one of the characteristics of reptiles.…”

Morphological and molecular evolution of the ultimobranchial gland of nonmammalian vertebrates, with special reference to the chicken C cells

“…Exceptionally, in monotremes, the most primitive subclass of mammals, the ultimobranchial body does not integrate into the thyroid primordium. Instead, it remains as a discrete organ lateral to the first or second ring of the cartilaginous trachea, just caudal to the larynx (Haynes, ). The ultimobranchial gland of monotremes consists of a mass of cells and small follicles.…”